Synthetic zeolites are crystalline aluminosilicate, and have uniform pores of a size in angstrom attributed to the crystal structure of each zeolite. Utilizing the characteristic, the synthetic zeolites have been industrially used as molecular sieve adsorbents for adsorbing only molecules having a specific size, adsorption separating agents for adsorbing highly affinitive molecules, and catalyst base. One of such zeolites, i.e., zeolite beta is abundantly used in the world as a catalyst in the petroleum chemical industry and an adsorbent for treating automobile exhaust gas. The characteristic of the zeolite beta is that the zeolite beta has pores of a 12-membered ring in a three-dimensional direction as described in Non Patent Literature 1 below. Moreover, the X-ray diffraction diagram showing the structural characteristics is described in Non Patent Literature 2 below.
A variety of processes for synthesizing a zeolite beta has been proposed. A general process uses tetraethylammonium ion as a structure directing agent (hereinafter abbreviated to an “SDA.”). Such a process is described in Patent Literature 1 and 3 and Non Patent Literature 3 below, for example. According to these processes, the zeolite beta having a SiO2/Al2O3 ratio 10 to 400 is obtained. Unfortunately, a compound containing tetraethylammonium ion is expensive, and most of it is decomposed after crystallization of the zeolite beta is completed. For this reason, the compound cannot be recovered and reused. For this reason, the zeolite beta produced by the process is expensive. Further, because tetraethylammonium ions are taken into crystals, the tetraethylammonium ions need to be calcined and removed when the zeolite beta produced by the process is used as an adsorbent or a catalyst. The exhaust gas in the calcination causes environmental pollution, and many chemicals are needed for the treatment for detoxifying a synthesis mother solution. Thus, the process for synthesizing a zeolite beta using tetraethylammonium ion is a production process that costs high and impose a large environmental load. Accordingly, realization of a production process without using the SDA has been desired.
In such a circumstance, Non Patent Literature 4 has recently proposed a process for synthesizing a zeolite beta with using no organic SDA. In the process, the zeolite beta synthesized using tetraethylammonium ion is calcined to remove an organic component, and the obtained product is used as a seed crystal. The seed crystal is added to a sodium aluminosilicate reaction mixture containing no organic substance, and a hydrothermal treatment is performed. Thus, crystallization is performed. In the process, however, because the zeolite beta synthesized using tetraethylammonium ion is calcined and the obtained product is used as a seed crystal, the amount of the SDA to be used is reduced while the tetraethylammonium ion as the SDA is always needed. Moreover, according to the process, the kind of the seed crystal is only one, and only one example of the composition of the sodium aluminosilicate reaction mixture is shown in which the numeric values are limited. Accordingly, although the composition of the synthesized zeolite beta is not clearly described, it is thought that the values of the composition are only determined ones.
On the other hand, Patent Literature 4 written by the author of Non Patent Literature 4 discloses a SiO2/Al2O3 ratio in a seed crystal and describes that the composition of a sodium aluminosilicate reaction mixture is not a point composition but in a narrow range from the point composition. Unfortunately, the disclosure of Patent Literature 4 is basically the same technique as the content of Non Patent Literature 4. The range of the composition of the reaction mixture is so narrow that the SiO2/Al2O3 ratio of the zeolite beta is limited to only a limited range. In order to deal with a variety of demands, a zeolite having a wide range of the SiO2/Al2O3 ratio is desired. Moreover, establishment of a condition allowing synthesis by stirring is desired for industrial mass production. Further, in order to reduce the environmental load as much as possible, a proposal of a new process for producing a zeolite beta is desired, in which a seed crystal not needed to be calcined is used and no organic SDA is used.